The invention relates to a method of manufacturing a multilayer printed circuit board, in which method conductors of different circuit layers are interconnected, by forming at least one depression in a first circuit layer at the location of the conductors to be interconnected, such that the relevant conductor of the first circuit layer contacts the relevant conductor or conductors of one or more other circuit layers.
A method of interconnecting printed circuit layers on opposite sides of an electrically insulating foil or of interconnecting two mutually insulated circuit layers of a printed circuit board is disclosed in U.S. Pat. No. 3,346,450. In this patent a depression technique is described in which a contact is formed between a first layer and a second layer without the second layer being pierced. The provisional connection thus formed must be electrically and mechanically reinforced by means of additional conductive material, for example, by plating copper or gold into the depression. In order not to penetrate the second layer, the method must be carried out against a hard backing surface which is not deformed during depression. In the method is applied to an electrically insulating foil provided with printed circuit layers, a hard backing surface is temporarily required. If it is applied to two circuit layers on one side of a printed circuit board the substrate should be sufficiently hard.